Shrimp and prawn cultivation and trade is a very important activity all over the world. The main species under cultivation are Penaeus monodon (Giant tiger prawn, Jumbo tiger prawn, Jumbo tiger shrimp, Black tiger prawn, Blue tiger prawn, Grass shrimp . . . ), mainly cultivated in Asia, with an aquaculture production of about 600,000 tons in 2003; and Penaeus vannamei (Whiteleg shrimp, white shrimp), mainly cultivated in the Americas and in China and Thailand, with an aquaculture production that is comparable to P. monodon. For those species, aquaculture is far more important than capture.
Increasing demands for aquaculture production mean increasing pressure for the development of more efficient production systems.
As most Penaeus sp. are sexually dimorphic (Hansford and Hewitt, 1994), a lot of effort has been paid in setting up monosex cultures. In that respect, several groups have tried to develop reliable sex markers (Khamnamtong et al., 2006). Alternatively, monosex cultures could be obtained by in vitro secretion of androgenic sex hormone from the androgenic gland, as disclosed in U.S. Pat. No. 6,740,794. Although this may be an interesting approach, it is hampered by the fact that the structure of the androgenic gland hormone, or of the gene encoding, is not known. Recently, Manor et al. (2007) described an insulin-like gene that is exclusively expressed in the androgenic gland of the male Australian Crayfish Cherax quadricarinatus. This may be an interesting candidate gene, possibly coding for the androgenic gland hormone, but its effect has not yet been demonstrated. Moreover, no homologues in prawns or shrimps are known today. Searching for homologous sequences is hampered by the fact that only a limited number of prawn and shrimp sequences are available in the databases, and by the fact that the interspecies homology is probably low, if any.
Surprisingly, in an AFLP-based transcriptomic profiling experiment in the black tiger shrimp (Penaeus monodon), we identified two androgenic gland-specific DNA fragments homologous to isopod “androgenic gland hormone” and crayfish “insulin-like androgenic gland” factor. By further cDNA sequencing and RACE experiments, we identified four mRNAs, termed PmAGH1, PmAGH2, PmAGH3 and PmAGH4, most probably originating from a single gene by alternative splicing. Even more surprisingly, treatment of genetically female juvenile shrimp using recombinant Pm_AGH1, Pm_AGH2, PmAGH3 and/or PmAGH4, had masculinizing effects. Genetically male juvenile shrimp were feminized by dsRNA-mediated knock-down of Pm_AGH1, Pm_AGH2, PmAGH3 and/or PmAGH4.